Chapter 12

• Sample


  A subset, or some part, of a larger population
• Population (Universe)


  Any complete group of entities that share some common set of characteristics
• Population Element


  An individual member of a population
• Census


  An investigation of all the individual elements that make up a population
• A puzzle is a sample until it is done! The sample allows one to guess at the picture.
• Reasons for sampling


  • Budget and time constraints
  • Limited access to total population
  • Accurate and reliable results
  • Destruction of test units
• Sampling Frame (Working Population)


  A list of elements from which a sample may be drawn
• Sampling Frame Error


  An error that occurs when certain sample elements are not listed or are not accurately represented in a sampling frame
• Sampling services (list brokers) provide lists or databases of the names, addresses, phone numbers, and e-mail addresses of specific populations
• Reverse Directory


  A directory similar to a telephone directory except that listings are by city and street address or by phone number rather than alphabetical by last name
• Online Panels


  Lists of respondents who have agreed to participate in marketing research along with the e-mail contact information for these individuals
• Availability of sampling frames varies dramatically around the world for international research
• Sampling Unit


  A single element or group of elements subject to selection in the sample
• Primary Sampling Unit (PSU)


  A term used to designate a unit selected in the first stage of sampling
• Secondary Sampling Unit


  A term used to designate a unit selected in the second stage of sampling
• Tertiary Sampling Unit


  A term used to designate a unit selected in the third stage of sampling
• Random Sampling Error


  The difference between the sample result and the result of a census conducted using identical procedures
• Primary Sampling Unit (PSU)


  A unit selected in the first stage of sampling
• Secondary Sampling Unit


  A unit selected in the second stage of sampling
• Tertiary Sampling Unit


  A unit selected in the third stage of sampling
• Random Sampling Error is a statistical fluctuation that occurs because of chance variations in the elements selected for a sample
• Systematic Sampling Error


  Systematic (nonsampling) error results from nonsampling factors, primarily the nature of a study's design and the correctness of execution
• Systematic Sampling Error is not due to chance fluctuation
• Opt In


  To give permission to receive selected e-mail, such as questionnaires, from a company with an Internet presence
• Random sampling errors and systematic errors associated with the sampling process may combine to yield a sample that is less than perfectly representative of the population
• Probability Sampling


  A sampling technique in which every member of the population has a known, non-zero probability of selection
• Non-Probability Sampling


  A sampling technique in which units of the sample are selected on the basis of personal judgment or convenience; the probability of any particular member of the population being chosen is unknown
• Convenience Sampling


  The sampling procedure of obtaining those people or units that are most conveniently available
• Judgment (Purposive) Sampling


  A non-probability sampling technique in which an experienced individual selects the sample based on personal judgment about some appropriate characteristic of the sample member
• Quota Sampling


  A non-probability sampling procedure that ensures that various subgroups of a population will be represented on pertinent characteristics to the exact extent that the investigator desires
• Possible sources of bias with Quota Sampling include respondents chosen because they were similar to interviewer, easily found, willing to be interviewed, middle-class, or needed to fill out the sample quota
• Advantages of Quota Sampling


  • Speed of data collection
  • Lower costs
  • Convenience
• Snowball Sampling


  A sampling procedure in which initial respondents are selected by probability methods and additional respondents are obtained from information provided by the initial respondents
• Simple Random Sampling


  A sampling procedure that assures each element in the population of an equal chance of being included in the sample
• Systematic Sampling


  A sampling procedure in which a starting point is selected by a random process and then every nth number on the list is selected
• Stratified Sampling


  A probability sampling procedure in which simple random subsamples that are more or less equal on some characteristic are drawn from within each stratum of the population
• Proportional Stratified Sampling


  A stratified sample in which the number of sampling units drawn from each stratum is in proportion to the population size of that stratum
• Disproportional Stratified Sampling


  A stratified sample in which the sample size for each stratum is allocated according to analytical considerations
• Stratified Sampling


  Simple random subsamples that are more or less equal on some characteristic are drawn from within each stratum of the population
• Proportional Stratified Sample: The number of sampling units drawn from each stratum is in proportion to the population size of that stratum